Device amd method for evaluating rigidity of bearing device, device and method for manufacturing bearing device, and bearing device

ABSTRACT

An apparatus of producing bearing device having a bearing, a shaft attached to an inner ring and an outer ring attaching member attached to an outer ring. The apparatus includes a vibrating unit of giving a radial input vibration to each inner ring or both ends of the shaft, and an input vibration detecting unit of detecting vibration of each inner ring or both ends of the shaft, an adding unit of calculating the output of the input vibration detecting unit, a vibration detecting unit of detecting the vibration of a mass attached to the outer ring attaching member, a transfer function calculating unit of determining the transfer function from the output of the vibration detecting unit and the adding unit to calculate the resonance frequency and a rigidity calculating unit of determining the rigidity of the bearing device on the basis of the resonance frequency.

TECHNICAL FIELD

The present invention relates to an apparatus and method of producing abearing device which can be preferably used for a bearing device thatmeet an important requirement for radial rigidity during use (resonanceproperties) such as bearing device for swing arm in magnetic disc (harddisc drive).

BACKGROUND ART

Recently, magnetic disc devices have been more and more required to havea high density, and the swing arm having a head forreproducing/recording signal mounted thereon has been required to makefaster access to the desired track and be positioned on the desiredtrack more accurately (speeding up and enhancement of precision ofpositioning). It has thus been desired to control the radial resonancefrequency of the bearing device for swing arm and eliminate thedispersion of rigidity of the bearing device.

In a controller (e.g., swing arm) having a bearing device incorporatedtherein, the dispersion of rigidity (resonance frequency) of the bearingdevice is one of factors causing the drop of efficiency of tuning ofservo system. Therefore, techniques and apparatus of predetermining therigidity (resonance frequency) of the bearing device to fall within apredetermined range have been considered important.

Patent Reference 1 cited below discloses a technique of controlling theradial resonance frequency of a bearing device for swing arm.

Further, Patent References 2, 3 and 4 cited below disclose a techniqueof determining the axial resonance frequency of a bearing device.

Moreover, Patent Reference 5 cited below discloses a method of producinga bearing device which includes press fitting while measuring theresonance frequency of the bearing device under the application ofvibration from a piezoelectric element and terminating press fittingwhen the resonance frequency thus measured reaches a predeterminedvalue.

[Patent Reference 1]

JP-A-2001-83045 (FIG. 1, page 3)

[Patent Reference 2]

Japanese Patent No. 2882105 (FIG. 1, pp. 4-5)

[Patent Reference 3]

JP-A-2000-146726 (FIG. 1, pp. 4-6)

[Patent Reference 4]

JP-A-2000-74788 (FIG. 1, pp. 4-5)

[Patent Reference 5]

JP-A-6-344233 (FIG. 1, pp. 4-6)

However, in accordance with the prior art apparatus and methods ofproducing a bearing device, the rigidity of the bearing device in theradial direction (radial rigidity) can difficultly be directlyevaluated.

In particular, the radial resonance frequency of a small-sized andlight-weight bearing device such as bearing device for swing arm candifficultly be accurately measured because such a bearing device has ahigh resonance frequency attributed to radial rigidity and a smallamplitude of resonance peak and the vibration mode of the measuringinstrument system and the bearing device are superposed on each other.Further, when the resonance frequency of a plurality of vibration modes(radial translation mode, conical mode) of the bearing device in theradial direction are close to each other, the accurate resonancefrequency cannot be determined, making it impossible to accuratelyevaluate radial rigidity.

Further, in accordance with the apparatus and method disclosed in PatentReference 5 cited above, the resonance frequency of the pivot can bedifficultly extracted from the vibration characteristics of the entireproduction device comprising the pivot to determine radial rigidity orresonance frequency in particular. The small size and light weight givean extremely high resonance frequency which, too, is a factor makingthis job difficult. This causes dispersion of resonance frequency,making it likely that the quality of the product thus produced can beunstable.

The present invention has been worked out under the circumstances andits aim is to provide a bearing device producing apparatus and methodcapable of producing a bearing device while accurately determining theradial rigidity thereof

DISCLOSURE OF THE INVENTION

The aim of the present invention is accomplished by the followingconstitutions.

(1) An apparatus of evaluating the rigidity of a bearing devicecomprising a bearing having an inner ring and an outer ring and an outerring attaching member attached to the outer ring, characterized in thatthere are provided a unit of giving an input vibration to the inner ringor a shaft attached to the inner ring, a vibration detecting unit ofdetecting the vibration of the outer ring attaching member or a massattached to the outer ring attaching member, a transfer functioncalculating unit of determining the transfer function from the output ofthe vibration detecting unit and the input vibration to calculate theresonance frequency of the bearing device and a rigidity calculatingunit of determining the rigidity of the bearing device on the basis ofthe resonance frequency calculated by the transfer function calculatingunit.

(2) An apparatus of evaluating the rigidity of a bearing devicecomprising a pair of bearings having an inner ring and an outer ring, ashaft attached to the inner ring and an outer ring attaching memberattached to the outer ring, characterized in that there are provided anvibrating unit of giving a radial input vibration to each of the innerrings or the both ends of the shaft, a pair of input vibration detectingunits of detecting the vibration of each of the inner rings or the bothends of the shaft, an adding unit of calculating the output of said pairof input vibration detecting unit, a vibration detecting unit ofdetecting the vibration of the outer ring attaching member or a massattached to the outer ring attaching member, a transfer functioncalculating unit of determining the transfer function from the output ofthe vibration detecting unit and the adding unit to calculate theresonance frequency of the bearing device and a rigidity calculatingunit of determining the rigidity of the bearing device on the basis ofthe resonance frequency calculated by the transfer function calculatingunit.

(3) A method of evaluating the rigidity of a bearing device comprising apair of bearings having an inner ring and an outer ring, a shaftattached to the inner ring and an outer ring attaching member attachedto the outer ring, which includes attaching a mass to the outer ring,giving a radial input vibration to each of the inner rings or the bothends of the shaft, detecting the vibration of each of the inner rings orthe both ends of the shaft to obtain a first detected vibration valueand a second detected vibration value, adding the first detectedvibration value and the second detected vibration value to obtain a sum,detecting the vibration of the outer ring attaching member or the massto obtain a third detected vibration value, determining the transferfunction from said third detected vibration value and the sum tocalculate the resonance frequency of the bearing device, and thendetermining the rigidity of the bearing device on the basis of saidresonance frequency.

(4) An apparatus of producing a bearing device comprising a bearinghaving an inner ring and an outer ring and an outer ring attachingmember attached to the outer ring, characterized in that there areprovided an vibrating unit of giving a radial input vibration to theinner ring or the shaft mounted thereon, a vibration detecting unit ofdetecting the vibration of the outer ring attaching member or a massattached to the outer ring attaching member, a transfer functioncalculating unit of determining the transfer function from the output ofthe vibration detecting unit and the input vibration to calculate theresonance frequency of the bearing device and a rigidity calculatingunit of determining the rigidity of the bearing device on the basis ofthe resonance frequency calculated by the transfer function calculatingunit.

(5) An apparatus of producing a bearing device comprising a pair ofbearings having an inner ring and an outer ring, a shaft attached to theinner ring and an outer ring attaching member attached to the outerring, characterized in that there are provided an vibrating unit ofgiving a radial input vibration to the inner ring or the shaft mountedthereon, a vibration detecting unit of detecting the vibration of theouter ring attaching member or a mass attached to the outer ringattaching member, a transfer function calculating unit of determiningthe transfer function from the output of the vibration detecting unitand the input vibration to calculate the resonance frequency of thebearing device and a rigidity calculating unit of determining therigidity of the bearing device on the basis of the resonance frequencycalculated by the transfer function calculating unit.

(6) A method of producing a bearing device comprising a pair of bearingshaving an inner ring and an outer ring, a shaft attached to the innerring and an outer ring attaching member attached to the outer ring,which includes attaching a mass to the outer ring, giving a radial inputvibration to each of the inner rings or the both ends of the shaft,detecting the vibration of each of the inner rings or the both ends ofthe shaft to obtain a first detected vibration value and a seconddetected vibration value, adding the first detected vibration value andthe second detected vibration value to obtain a sum, detecting thevibration of the outer ring attaching member or the mass to obtain athird detected vibration value, determining the transfer function fromsaid third detected vibration value and the sum to calculate theresonance frequency of the bearing device, and then determining therigidity of the bearing device on the basis of said resonance frequency.

(7) An apparatus of producing a bearing device comprising a bearinghaving an inner ring and an outer ring and a housing fitted on the outerring, characterized in that at least one of radial rigidity, resonancefrequency and anti-resonance frequency is detected and when the valuethus detected reaches a predetermined value, press fitting isterminated.

(8) The apparatus of producing a bearing device as described in Clause(7), wherein there are provided an vibrating unit of giving radialvibration to the inner ring or a shaft fitted in said inner ring, aloading unit for press fitting, a vibration detecting unit of detectingthe vibration at least one site on the shaft or inner ring and thehousing or outer ring and an operation controlling unit of determiningthe rigidity, resonance frequency or anti-resonance frequency of thebearing device from the signal detected by the vibration detecting unit.

(9) The apparatus of producing a bearing device as described in Clause(7) or (8), wherein there is provided a transfer function calculatingunit to determine resonance frequency.

(10) A method of producing a bearing device which includes using aproduction apparatus as described in any one of Clauses (7) to (9) toproduce a bearing device.

(11) A bearing device having a radial rigidity predetermined by aproduction method as described in Clause (6) or (10).

In accordance with the constitutions, the transfer function concerningthe vibration in the direction of deformation of the bearing device canbe determined to accurately determine the radial rigidity of the bearingdevice.

In accordance with the constitutions, isophase and isoamplitudecomponents (vibration components developed at sites other than bearingdevice) detected at each of the inner and outer rings can be separatedfrom each other to extract the vibration properties of the bearingdevice alone. In particular, when a mass is attached to the outer ringattaching member to increase the weight and moment of inertia of themovable portion comprising the outer ring and the outer ring attachingmember, the detection of resonance peak can be easily conducted. This isbecause the rise of the weight of the movable portion makes it possibleto reduce the resonance frequency due to radial rigidity and raise theamplitude of resonance peak. Further, the rise of the moment of inertiaallows effective reduction of the resonance frequency of the bearingdevice in conical mode, making it possible to increase the differencefrom the resonance frequency in radial translation mode and henceconduct accurate measurement of resonance frequency.

Moreover, in accordance with the constitutions, the radial rigidity orresonance frequency of the bearing device can fall within apredetermined range, making it easy to effect tuning of the servo systemwhen the bearing device is incorporated in, e.g., a swing arm. Further,the precision in measurement of radial rigidity or resonance frequencycan be drastically enhanced. Moreover, the enhancement of the precisionin measurement of radial rigidity or resonance frequency makes itpossible to stabilize the quality of a pivot which has been press-fittedin resonance mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general view of an apparatus of producing a bearing deviceaccording to a first embodiment of implementation of the presentinvention.

FIG. 2 is a graph illustrating the effect developed by adding a mass inthe first embodiment.

FIGS. 3A and 3B are graphs illustrating the frequency characteristics ofa transfer function in the first embodiment.

FIGS. 4A to 4C are diagrams illustrating a method of attaching a mass tothe bearing device of the first embodiment.

FIG. 5 is a diagram illustrating a modification of the first embodiment.

FIG. 6 is a graph illustrating the effect of another modification.

FIG. 7 is a general view of an apparatus of producing a bearing deviceaccording to a second embodiment of implementation of the invention.

FIG. 8 is a diagram of frequency characteristics developed aftercalculation of FFT transfer function in the second embodiment.

FIG. 9 is a conceptional diagram of transfer function which is avibration model in the second embodiment.

FIGS. 10A and 10B is a diagram illustrating the radial vibration mode ofa pivot in the second embodiment.

FIGS. 11A to 11E are diagrams illustrating a method of attaching a massin the second embodiment.

FIG. 12 is a general view of a modification of the second embodiment.

FIG. 13 is a general view of another modification of the secondembodiment.

FIG. 14 is a diagram of waveform measured in the modification shown inFIG. 13.

FIG. 15 is a general view of other modification in the secondembodiment.

FIG. 16 is a general view of further modification in the secondembodiment.

In these figures, the reference numeral 1 indicates a support portion,the reference numeral 2 indicates an vibrating portion, the referencenumeral 3 indicates a vibration detecting portion, the reference numeral4 indicates an operation processing portion, the reference numeral 5indicates a bearing device, the reference numerals 10 and 60 eachindicate an apparatus of producing a bearing device, the referencenumeral 23 a indicates a piezo electric element type vibrator (vibratingunit), the reference numerals 31 a to 31 c each indicate a vibrationdetecting sensor (vibration detecting unit), the reference numeral 33indicates an adder (adding unit), the reference numeral 41 indicates atransfer function calculating unit (rigidity calculating unit), thereference numeral 43 indicates a rigidity conversion device, thereference numeral 51 indicates a housing (outer ring attaching member),the reference numeral 52 indicates a shaft, the reference numeral 53indicates a rolling bearing, and the reference numeral 54 indicates amass.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of implementation of the present invention will be describedin detail in connection with the drawings.

In the second and following embodiments, the members having the sameconstitution and action as that of those described already will be giventhe same reference numerals and signs in figures to simplify or omittheir description.

As shown in FIG. 1, the apparatus 10 of producing a bearing device ofthe first embodiment mainly include a rigidity evaluation device 10 ahaving a support portion 1 of supporting and fixing the bearing device 5in the axial direction, an vibrating portion 2 of vibrating the bearingdevice 5 in the radial direction, a vibration detecting portion 3 ofdetecting the radial vibration of the bearing device 5 and an operationprocessing portion 4 of evaluating the radial rigidity of the bearingdevice 5 on the basis of the output of the vibration detecting portion3.

Herein, the bearing device 5 has two ball bearings 53, 53 disposedaxially apart from each other, a shaft 52 fitted in the inner ringthereof and a housing (outer ring attaching member) 51 fitted on theouter ring thereof. The mass 54 is attached to the periphery of thehousing 51. The weight of the mass 54 may be the same as the loadactually applied to a device (e.g., swing arm bearing device formagnetic disc device) in which the bearing device 5 is incorporated. Theshape (center of gravity, moment of inertia) of the mass 54, too, maybeequivalent to that of parts (e.g., swing arm) actually born by thebearing device 5.

A supporting portion 1 has a loading device 11 disposed on one end(upper end) of the shaft 52 to give a fixing power to the shaft 52 ofthe bearing device 5 and load cell (load sensor) 12 disposed on theother end (lower end) of the shaft 52 to monitor the load. In thisarrangement, the shaft 52 can be fixed at a constant load. The loadingdevice 11 and the load cell 12 may be disposed on the same side of thebearing device 5. A supporting part 24 a and an a vibrator 23 adescribed later are disposed interposed between one end of the shaft 52and the loading device 11 while a supporting part 24 b and a vibrator 23b are disposed interposed between the other end of the shaft 52 and theload cell 12. Since the state of fixing of the both ends of the shaft 52to the supporting parts 24 a, 24 b affects the results of evaluation ofradial rigidity, it is desired that the shaft 52 be fixed at a properload by the loading device 11 and the load cell 12.

The vibrating portion 2 has an oscillator 21 of generating a voltagewaveform in which sinusoidal wave sweeps at a high speed with apredetermined frequency range, a pair of piezoelectric element typevibrators 23 a, 23 b of generating an vibrating force at an amplitudeand frequency corresponding to the voltage waveform generated by theoscillator 21 and an amplifier 22 disposed interposed between theoscillator 21 and the vibrators 23 a, 23 b. When the pair of vibrators23 a, 23 b vibrate at the same phase in the radial direction, radialvibration is given to the bearing device 5. The vibration excited in thebearing device 5 includes radial translation mode attributed to theradial rigidity of the bearing device 5 (mode of vibration based on thetranslation of radial rigidity of the housing 51 and the elastic flexingof the shaft 52), conical mode (mode of vibration based on theinclination of the housing 51), elastic vibration mode of parts of thebearing device 5 and vibration mode came from the measuring instrumentsystem including the supporting portion 1 and the vibration portion 2superposed on each other.

The vibration detecting portion 3 has a vibration detecting sensor 31 cdisposed at the axially central position between the housing 51 and themass 54 and vibration detecting sensors 31 a, 31 b disposed on thesupporting parts 24 a, 24 b at the both ends of the shaft 52,respectively. These vibration detecting sensors 31 a, 31 b, 31 c aredisposed on the same plane including the axial direction of the shaft52. As the vibration detecting sensors 31 a, 31 b and 31 c there may beused properly a piezoelectric element type sensor, a laser non-contacttype sensor, a record pick up, etc. The vibration detected by thevarious vibration detecting sensors 31 a, 31 b and 31 c includes thevarious modes superposed on each other. The output signal of thevibration detecting sensors 31 a, 31 b on the both ends of the shaft 52(first detected vibration value, second detected vibration value),respectively, are amplified by amplifiers 32 a, 32 b, and then added atthe adder 33. This addition causes the conical vibration component ofthe shaft 52 to be eliminated, giving a signal of translation mode ofthe shaft 52.

The signal outputted from the adder 33 is an added signal and thus isamplified by a main amplifier 34 b. Thereafter, the level (amplitude) ofthe signal is halved.

The operation processing portion 4 has a transfer function calculatingunit 41 which receives an output signal (third detected vibration value)from the vibration detecting sensor 31 c via an amplifier 34 a as wellas an output signal from the adder 33 via the amplifier 34 b. Thetransfer function calculating unit 41 makes the use of fast Fouriertransform (FFT) to calculate the resonance frequency (characteristicfrequency) fr of the bearing device 5. In some detail, the transferfunction H of the inner and outer rings (between shaft 52 and housing51) is calculated by FFT to cause isophase and isoamplitude vibratingcomponents included in the various signals inputted to be separated andhence cause radial resonance frequency fr to appear at a phasedifference of π/2. At this point, since the vibration detecting sensor31 c observes the axial center between the housing 51 and the mass 54,conical mode in which the component falls and vibrates with the axialcenter of the housing 51 as a node can be difficultly detected and theradial translation mode is mainly detected.

The timing at which the oscillator 21 of the vibrating portion 2generates a voltage waveform and the timing at which the transferfunction calculating unit 41 of the operation processing portion 4performs sampling are completely synchronized.

In the present embodiment, the mass 54 is attached to the housing 51 ofthe bearing device 5 to reduce the resonance frequency as compared withthe case where no mass is added (bearing device alone) as shown in FIG.2. Further, the addition of the mass 54 makes the difference inresonance frequency between radial translation mode and conical modeabout 10 times that in the case of bearing device alone.

FIGS. 3A and 3B illustrate the frequency characteristics of transferfunction H calculated by the rigidity evaluation device 10 a. FIG. 3Aillustrates the phase difference and FIG. 3B illustrates the amplitude(gain).

When the bearing 53 of the bearing device 5 is free of seal or grease,the attenuation possessed by the bearing 53 is negligibly small andthere is no difference in evaluation of rigidity between by themeasurement of frequency at which the phase difference of transferfunction H is −π/2 and by the measurement of frequency at which theamplitude is at peak.

However, when the bearing 53 of the bearing device 5 is provided with aseal or filled with a grease, the attenuation possessed by the bearing53 is not negligible. In this case, the dispersion of frequency at whichthe amplitude is at peak increases. Nevertheless, there occurs nodispersion in the frequency at which the phase difference is −π/2, andevaluation by the phase difference can be conducted to maintain theprecision in rigidity evaluation in the present invention.

The waveform of FIGS. 3A, 3B is displayed on a waveform display 42 asshown in FIG. 1. Further, the radial resonance frequency fr determinedis inputted to the rigidity conversion device 43. Since the relationshipbetween the radial resonance frequency and the radial rigidity of thebearing device is nonlinear and the radial rigidity cannot be directlydetermined from the radial resonance frequency, the following method isemployed. The rigidity conversion device 43 performs FEM (Finite ElementMethod) analysis to approximate the relationship between the previouslydetermined radial rigidity and radial resonance frequency fr of thebearing device by a polynomial and then uses the polynomial to calculatethe radial rigidity Kr of the bearing device with respect to the radialresonance frequency fr inputted. In some detail, since Kr=f(fr, α) isdefined as a function indicating the relationship between radialrigidity Kr and resonance frequency fr, contact angle α is previouslysubjected to FEM analysis to determine a discrete value from which thefunction is approximated by a polynomial having resonance frequency fras a variable. Using this polynomial, measured resonance frequency frcan be converted to radial rigidity Kr.

In the case where the radial rigidity Kr of the bearing device thusdetermined falls below or exceeds the predetermined value, the radialrigidity of the bearing device is optimized by re-predetermining thepreload or otherwise.

Next, a method of attaching the mass 54 to the housing 51 of the bearingdevice 5 will be described in connection with FIGS. 4A to 4C.

In the example shown in FIG. 4A, the mass 54 is formed by two members,i.e., first portion 54 a and second portion 54 b. The steppedcylindrical first 54 a having an inwardly protruding flange 54 cprovided at the end on the large diameter side thereof is attached tothe periphery of the housing 51, and the cylindrical second portion 54 bis threaded onto or otherwise attached to the periphery of the smalldiameter portion of the first portion 54 a. There is provided a flange54 d also at the other end of the second portion 54 b, and the flange 54d and the flange 54 c of the first portion 54 a clamp and fix thehousing 51 and the pair of bearings 53, 53 along the shaft. Since theaxial deformation of the housing 51 by the effect of clamping and fixingcan change the preload in the bearing device 5, it is desired that thedeformation be previously determined for correction.

In the example shown in FIG. 4B, the cylindrical mass 54 is screwed onthe periphery of the housing 51. Herein, the radially extending hole ofthe mass 54 is threaded such that when a screw 59 is driven, the mass 54moves inwardly. Since the contact of the periphery of the housing 51with the inner surface of the mass 54 or the deformation of the housing51 by the axial force of the screw 59 greatly affects the evaluation ofradial rigidity, it is desired that the screw 59 be driven with a propertorque.

In the example shown in FIG. 4C, the axial hole of the mass 54 forms atapered hole the inner surface of which is bitten by one end face of thehousing 51 which is a chamfered surface so that the mass 54 is fixed tothe housing 51. In this case, too, since the contact of the mass 54 withthe chamfered portion of the housing 51 affects the evaluation of radialrigidity, it is desired that the fixing conditions be stabilized byproviding a guide portion or otherwise so that the insert force can becontrolled to keep the shaft 52 and the mass 54 coaxial.

In the embodiments, as shown in FIG. 1, the output signal from thevibration detecting sensor 31 c is inputted to the transfer functioncalculating unit 41 via the amplifier 34 a while the output signal fromthe adder 33 is inputted to the transfer function calculating unit 41via the amplifier 34 b.

However, the present invention is not limited to these embodiments, andhigh pass filters 35 a, 35 b can be provided interposed between theamplifiers 34 a, 34 b and the transfer function calculating unit 41 asshown in FIG. 5. In this arrangement, unnecessary frequency componentsof external noises such as power supply noise can be cut off to enhanceS/N ratio. The constitutions which are no shown in FIG. 5 may be similarto that of FIG. 1.

Further, in the embodiments, the rigidity evaluation device 43 performsFEM analysis to approximate the relationship between the previouslydetermined radial rigidity and radial resonance frequency fr of thebearing device 5 by a polynomial by which the radial rigidity Kr of thebearing device with respect to the radial resonance frequency inputtedis calculated. However, the present invention is not limited to theseembodiments, and on the basis of, e.g., a supposed one-freedom modelcomprising the weight M of the movable portion consisting of the outerring and housing 51 of the bearing 53 and the mass 54 and a springhaving a radial rigidity Kr, the radial rigidity Kr can be easilydetermined from the resonance frequency fr in the rigidity conversiondevice 43. In the model, the radial rigidity Kr is represented by:Kr=4M(πfr)2Substituting M which has been previously determined from the outer ring,the housing 51 and the mass 54 and measured fr for M and fr,respectively, in the equation yields the radial rigidity Kr.

FIG. 6 is a graph illustrating the comparison of radial rigiditydetermined by the use of FEM analysis with radial rigidity determined bythe use of one-freedom model. Thus, the two models have a highrelationship to give a very small error.

By determining the transfer function concerning the vibration of thebearing device 5 in the direction of deformation, the radial rigidity ofthe bearing device 5 can be accurately determined.

In accordance with the apparatus 10 of producing a bearing deviceaccording to a first embodiment, isophase and isoamplitude components(vibration components developed at sites other than bearing device)detected at each of the inner and outer rings can be separated from eachother to extract the vibration properties of the bearing device alone.In particular, when the mass 54 is attached to the housing 51 toincrease the weight and moment of inertia of the movable portioncomprising the outer ring and the housing 51, the detection of resonancepeak can be easily conducted. This is because the rise of the weight ofthe movable portion makes it possible to reduce the resonance frequencydue to radial rigidity and raise the amplitude of resonance peak.Further, the rise of the moment of inertia allows effective reduction ofthe resonance frequency of the bearing device 5 in conical mode, makingit possible to increase the difference from the resonance frequency inradial translation mode and hence conduct accurate measurement ofresonance frequency.

Next, an apparatus of producing a bearing device according to a secondembodiment of implementation of the present invention will be described.

As shown in FIG. 7, in the apparatus 60 of producing a bearing deviceaccording to the second embodiment, a pair of vibrators 23 a, 23 b applyradial vibration to the both ends of a pivot via a press fitting fixture61. As the vibrators 23 a, 23 b there are preferably used those having asufficient strength and rigidity in the axial direction, e.g., piezoelectric element or magnetostrictive element. The vibration signalgenerated by the vibrators 23 a, 23 b results in good swept sinusoidalsignal.

On vibrator 23 a is connected to a direct acting loading device 11 suchas hydraulic or feed screw mechanism while the other vibrator 23 b isconnected to the load cell 12, making it possible to detect the pressfitting force. The press fitting force is fed back to control the feedrate and is used also for correction of measurements as described later.

The vibration sensors 31 a, 31 b and 31 c are disposed on the both endsof the shaft 52 or on the press fitting fixture 61 and the housing 51 oron the periphery of the outer ring. The vibration sensors 31 a, 31 b and31 c are linearly disposed on the same plane as that of the vibratingdirection.

The vibration sensors 31 a, 31 b and 31 c each may be of fixed type suchas acceleration pickup, feeler type such as record needle or non-contacttype such as laser Doppler speedometer.

The two signals from the respective ends of the shaft are added to eachother, halved in level, passed through a filter, subjected to ADconversion, and then subjected to FFT analysis. The addition causessubtraction of vibration components which are out of phase from eachother at the both ends of the shaft, and the signal thus processed isequivalent to the vibration signal at the center of the shaft 52. Thissignal is supposed to be an input signal Xa.

The signal from the housing 51 or the outer ring is subjected to thesame processing as described above (no addition) This is supposed to bea response signal Xb.

Using the following equation, a transfer function is calculated from theinput signal Xa and the response signal Xb. Herein, Xb* is a conjugatedcomplex number.H(jω)=Xb×Xb*/Xa×Xb*

As shown in FIG. 8, the frequency characteristics of gain and phasedifference obtained from the results of calculation show that thefrequency at which the gain peak or phase difference is −90° is theresonance frequency of the pivot.

By detecting the vibration of the two masses (inner ring and outer ringin this case) opposed to each other via bearing rigidity and determiningthe transfer function therebetween, only the frequency characteristicsof a local system includes bearing rigidity and weight of outer ring andhousing 51 can be extracted for evaluation.

The effect is represented in the vibration model shown in FIG. 9.

Referring to a method of determining rigidity from resonance frequency,rigidity is represented by the following equation.f=(½π)×{square root}(k/M)

Substituting known weight M and determined resonance frequency f in Mand f, respectively, in the equation yields rigidity k.

Alternatively, a relationship between bearing rigidity andcharacteristic frequency which has been previously established by anumerical analysis such as finite element method may be used.

During press fitting, the load corresponding to press fitting force actson the shaft 52, causing the change of solid preload and hence deviatingthe resonance frequency from the unloaded value. Therefore, the measuredvalue is subjected to correction for shaft load. Using the load Fdetected by the load cell 12, the normal frequency is determined by thefollowing equation.Fr=C(F)×iwherein Fr is the normal frequency; F is the frequency measured; andC(F) is a correction coefficient.

In accordance with the second embodiment, the radial rigidity orresonance frequency of the bearing device is allowed to fall within apredetermined range, making it easy to perform tuning of servo systemwhen the bearing device is incorporated in, e.g., a swing arm. Further,the precision in measurement of radial rigidity or resonance frequencycan be drastically enhanced. Moreover, the enhancement of precision inmeasurement of radial frequency or resonance frequency makes it possibleto stabilize the quality of a pivot which has been press-fitted inresonance mode.

A modification of the second embodiment will be described hereinafter.

Any resonance frequency may be measured so far as it appears in theradial direction of the pivot.

For example, there is a translation mode shown in FIG. 10A or a rigidbody mode called conical mode shown in FIG. 10B.

An additional mass may be added. The effect of such an additional massis to increase the weight of the outer ring, lowering the resonancefrequency of the bearing device 5 and hence making it possible toevaluate the resonance frequency within a low frequency range givinglittle effect of noise. Further, the amplitude during resonance isamplified, making it easy to detect peak.

At the same time, the moment of inertia of the outer ring is increasedto lower the characteristic frequency of conical mode. Even in the casewhere the characteristic frequency in translation mode and conical modeare close to each other and thus can difficultly be individuallydistinguished in normal operation, they can be easily distinguished fromeach other by making these characteristic frequencies different.

In order to decide the shape of the additional mass, it is effective totune the weight, moment of inertia and center of gravity such that theindividual modes have a desired resonance frequency. For example, it ispreferred that the center of gravity be at the center of the bearingspan.

Since the rigidity (contact rigidity) of the additional mass mountingportion affects the resonance frequency of the pivot, a method of firmlyfixing the additional mass is. preferably used.

Using a swing arm main body attached to the bearing device instead ofadditional mass, evaluation may be conducted under actual workingconditions.

FIGS. 11A, 11B, 11C, 11D and 11E each illustrate a method of mountingthe additional mass.

In FIG. 11A, the inner hole of a cylindrical additional mass 54 is atapered hole 54 e which is bitten by the chamfered portion of the outerring or housing 51. In accordance with this mounting method, the pushingforce is controlled, making it possible to fix the additional mass 54 tothe bearing device 5 firmly and stably. This case is similar to FIG. 4C.

In FIG. 11B, a straight portion 54f is formed in a part of the taperedhole 54e so that the additional mass 54 can be prevented from beingfixed inclined.

FIG. 11C illustrates a cylinder including two divisions which clamp theends of the bearing device. This case is similar to FIG. 4A.

In FIG. 11D, a cylindrical additional mass is fixed to the side of thehousing with a screw. In this case, screw fixing may be replaced byadhesion. This case is similar to FIG. 4A.

In FIG. 11E, the radial expansion and shrinkage of a hollow cylindricalpiezoelectric element 62 is utilized.

FIG. 12 illustrates a modification involving the elimination or drivingof any one of the upper and lower vibrators. In this case, only onevibrator 23 a is used.

The driving mode can be freely excited also by arranging such that theupper and lower vibrators can be driven at individual amplitudes andphases. In general, the upper and lower vibrators are driven at the samephase and amplitude.

FIG. 13 illustrates a modification involving the detection of only thevibration signal Xa of the both ends of the shaft or the press fitting61 from which anti-resonance frequency is determined.

FIG. 14 illustrates the waveform of measurements in the presentmodification.

In this case, the vibration amplitude of the housing 51 and the outerring becomes maximum at the resonance frequency of the bearing device 5,and the system in resonance acts as a dynamic vibration absorber to dampthe vibration of the inner ring and the shaft 52, minimizing theamplitude and hence keeping anti-resonance. Therefore, by detecting thevibration of only the inner ring and the shaft 52 and then determiningthe anti-resonance frequency, the same effect as that by determining theresonance frequency of the bearing device 5 can be exerted. In thisarrangement, the number of sensors or circuits can be reduced, making itpossible to reduce cost.

Referring to another modification which is a simple method, resonancefrequency can be determined from time axis data.

In this case, a transfer function is determined from two signals in atime range. The resonance frequency can be estimated from therelationship between the amplitude of the transfer function and thepreviously determined amplitude and resonance frequency of the system.This can be applied also to the anti-resonance method.

The effect of this method is to eliminate the necessity of FFT and hencespeed up calculation. This leads to cost reduction and recyclabilityenhancement. The time required to judge resonance frequency can bereduced, making it possible to enhance the precision in positioning ofpress fitting and reduce the dispersion of rigidity.

Further, as other modification, the vibration unit may be modified.

To this end, a method involving the vibration of the entire device inthe radial direction or a method involving the vibration of the housing51 may be used.

For example, a method which includes hitting the housing 51, a methodwhich includes striking the vibrators 23 a, 23 b against the housing 51,a method which includes applying sound wave to the housing 51 to vibratethe housing 51 in non-contact process, a method which includes applyinga magnetic field from an outer ring which is a coil to the housing 51,etc. may be used.

As shown in FIG. 15, the housing 51 can be press-fitted to the bearingdevice 5 while determining the static radial rigidity of the bearingdevice 5 from the displacement measured at a static load using Hooke'sLaw.

In this case, the displacement of the housing 51, the inner ring and theshaft 52 is measured by a contact type or non-contact type displacementmeter while the housing 51 or the outer ring is being under static load.Displacement meters 63 a, 63 b and 63 c are disposed at the positionscorresponding to that of the vibration sensors 31 a, 31 b and 31 c.

For measurement, the following equation is used.F=K(x2−x1)wherein F is the load; x1 is the displacement of the loaded point; andx2 is the displacement of the shaft and inner ring.

Measurement and press fitting can be conducted while rotating the outerring.

In this case, the circumferential dispersion of rigidity which can occurdue to precision in ball position, race, etc. can be evaluated.

Further, as a resonance measuring function, vibration and measurementmay be conducted on the press fitting device while fixing the work atthe press fitting force or less. In this case, a structure for clampingthe ends of the shaft is used instead of the press fitting fixture.Other mechanisms may be the same as the structure according to thesecond embodiment.

As shown in FIG. 16, the press fitting mold (loading device) 64 may bestruck against the inner ring on the periphery thereof while the ends ofthe shaft are clamped by the vibrators 23 a, 23 b. In this case, thevarious loading devices are separate mechanisms by which the clampingforce and the press fitting force can be separately controlled.

In general, an article having a small press fitting force cannot beprovided with a sufficient clamping force. In this case, the vibrationforce cannot be thoroughly transferred to this article. Further, thecontact rigidity of the press fitting type bearing device supportingportion is reduced, making it impossible to measure correct resonancefrequency. In this arrangement, however, an article having a small pressfitting force can be provided with a sufficient clamping force, makingit possible to determine correct resonance frequency.

The present invention is not limited to the embodiments and can beproperly modified, improved or otherwise changed.

For example, the various modifications may be combined as necessary.

The bearing device is not limited to ball bearing but may be acylindrical roller bearing or tapered roller bearing.

While the present invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

The present application is based on Japanese Patent Application No.2001-311501, filed on Oct. 9, 2001 and the contents thereof areincorporated herein by reference.

<Industrial Applicability>

As mentioned above, in accordance with the present invention, thetransfer function concerning the vibration of the bearing device in thedirection of deformation is determined, making it possible to accuratelydetermine the radial rigidity of the bearing device.

Further, in accordance with the present invention, isophase andisoamplitude vibration components (vibration components other thanvibration attributed to the rigidity of the bearing device) included inthe vibration of each of the inner and outer rings are separated fromeach other to determine radial resonance frequency (characteristicfrequency). In particular, when a mass is attached to the outer ringattaching member to increase the weight and moment of inertia of themovable portion comprising the outer ring and the outer ring attachingmember, the detection of resonance peak can be easily conducted. This isbecause the rise of the weight of the movable portion makes it possibleto reduce the resonance frequency due to radial rigidity and raise theamplitude of resonance peak. Further, the rise of the moment of inertiaallows effective reduction of the resonance frequency of the bearingdevice in conical mode, making it possible to increase the differencefrom the resonance frequency in radial translation mode and henceconduct accurate measurement of resonance frequency.

Moreover, the radial rigidity or resonance frequency of the bearingdevice can fall within a predetermined range, making it easy to effecttuning of the servo system when the bearing device is incorporated in,e.g., a swing arm. Further, the precision in measurement of radialrigidity or resonance frequency can be drastically enhanced. Moreover,the enhancement of the precision in measurement of radial rigidity orresonance frequency makes it possible to stabilize the quality of apivot which has been press-fitted in resonance mode.

Thus, a bearing device producing apparatus and method capable ofproducing a bearing device while accurately determining the radialrigidity thereof can be provided.

1-11. Canceled
 12. An apparatus for evaluating a rigidity of a bearingdevice including a bearing having an inner ring, a shaft attached to theinner ring, an outer ring and an outer ring attaching member attached tothe outer ring, comprising: a mass attached to the outer ring attachingmember; an input vibration unit for giving a radial input vibration toone of the inner ring and the shaft attached to the inner ring; avibration detecting unit for detecting a vibration of one of the outerring attaching member and the mass; a transfer function calculating unitfor calculating a transfer function from an output of the vibrationdetecting unit and the radial input vibration to determine a resonancefrequency of the bearing device; and a rigidity calculating unit fordetermining a rigidity of the bearing device on the basis of theresonance frequency of the bearing device determined by the transferfunction calculating unit.
 13. An apparatus for evaluating a rigidity ofa bearing device including a pair of bearing having an inner ring and anouter ring, a shaft attached to the inner ring and an outer ringattaching member attached to the outer ring, comprising: a mass attachedto the outer ring attaching member; an input vibration unit for giving aradial input vibration to one of the each inner ring and both ends ofthe shaft attached to the inner ring; a pair of vibration detectingunits for detecting a vibration of one of the each inner ring and theboth ends of the shaft attached to the inner ring; an adding unit foradding an output of the pair of vibration detecting units; a vibrationdetecting unit for detecting a vibration of one of the outer ringattaching member and the mass; a transfer function calculating unit forcalculating a transfer function from an output of the vibrationdetecting unit and the output of the adding unit to determine aresonance frequency of the bearing device; and a rigidity calculatingunit for determining a rigidity of the bearing device on the basis ofthe resonance frequency of the bearing device determined by the transferfunction calculating unit.
 14. A method for evaluating a rigidity of abearing device including a pair of bearing having an inner ring and anouter ring, a shaft attached to the inner ring and an outer ringattaching member attached to the outer ring, comprising the steps of:attaching a mass to the outer ring; giving a radial input vibration toone of each inner ring and both ends of the shaft attached to the innerring; detecting a vibration of the one of each inner ring and both endof the shaft attached to the inner ring so that a first vibrationdetecting value and a second vibration detecting value are obtained;adding the first vibration and the second vibration so that an addedvalue of the first vibration detecting value and the second vibrationdetecting value is obtained; detecting a vibration of one of the outerring attaching member attached to the outer ring and the mass so that athird vibration detecting value is obtained; calculating a transferfunction from the third vibration detecting value and the added value sothat a resonance frequency of the bearing device is determined; andcalculating a rigidity of the bearing device from the transfer function.15. An apparatus for producing a bearing device including a bearinghaving an inner ring, a shaft attached to the inner ring, an outer ringand an outer ring attaching member attached to the outer ring,comprising: an input vibration unit for giving a radial input vibrationto one of the each inner ring and the shaft; a vibration detecting unitfor detecting a vibration of one of the outer ring attaching member anda mass attached to the outer ring attaching member; a transfer functioncalculating unit for calculating a transfer function from an output ofthe vibration detecting unit and the radial input vibration to determinea resonance frequency of the bearing device; and a rigidity calculatingunit for determining a rigidity of the bearing device on the basis ofthe resonance frequency of the bearing device determined by the transferfunction calculating unit.
 16. An apparatus for producing a bearingdevice including a pair of bearing having an inner ring and an outerring, a shaft attached to the inner ring, and an outer ring attachingmember attached to the outer ring, comprising: a mass attached to theouter ring attaching member; an input vibration unit for giving a radialinput vibration to one of each inner ring and both ends of the shaftattached to the inner ring; a pair of vibration detecting units fordetecting a vibration of one of the each inner ring and the both ends ofthe shaft attached to the inner ring; an adding unit for adding anoutput of the pair of vibration detecting units; a vibration detectingunit for detecting a vibration of one of the outer ring attaching memberand the mass; a transfer function calculating unit for calculating atransfer function from an output of the vibration detecting unit and theoutput of the adding unit to determine a resonance frequency of thebearing device; and a rigidity calculating unit for determining arigidity of the bearing device on the basis of the resonance frequencyof the bearing device determined by the transfer function calculatingunit.
 17. A method for producing a bearing device including a pair ofbearing having an inner ring and an outer ring, a shaft attached to theinner ring and an outer ring attaching member attached to the outerring, comprising the steps of: attaching a mass to the outer ring;giving a radial input vibration to one of each inner ring and both endsof the shaft attached to the inner ring; detecting a vibration of one ofthe each inner ring and the both ends of the shaft attached to the innerring so that a first vibration detecting value and a second vibrationdetecting value are obtained; adding the first vibration and the secondvibration so that an added value of the first vibration detecting valueand the second vibration detecting value is obtained; detecting avibration of one of the outer ring attaching member attached to theouter ring and the mass so that a third vibration detecting value isobtained; calculating a transfer function from the third vibrationdetecting value and the added value so that a resonance frequency of thebearing device is determined; and calculating a rigidity of the bearingdevice from the transfer function.
 18. An apparatus for producing abearing device including a bearing having an inner ring, a shaftattached to the inner ring, an outer ring and a housing fitted to theouter ring, comprising: a detecting unit for detecting at least one of aradial rigidity, a resonance frequency and an anti-resonance frequency;wherein a press-fitting operation is finished when the at least one ofthe radial rigidity, the resonance frequency and the anti-resonancefrequency become a predetermined value.
 19. The Apparatus for producinga bearing device including a bearing having an inner ring, a shaftattached to the inner ring, an outer ring and a housing fitted to theouter ring according to claim 18, further comprising: an input vibrationunit for giving a radial vibration to one of the inner ring and a shaftinwardly fitted to the inner ring; a loading unit for press-fitting; avibration detecting unit for detecting a vibration of at least one ofone of the each inner ring and the shaft and one of the outer ring andthe housing; and a calculating control unit for calculating one of arigidity of the bearing device and both a resonance frequency and ananti-resonance frequency from a signal detected by the vibrationdetecting unit.
 20. The Apparatus for producing a bearing deviceincluding a bearing having an inner ring and an outer ring and a housingfitted to the outer ring according to claim 18, further comprising: atransfer function calculating unit for calculating a transfer function.21. A method for producing a bearing device, comprising the step of:producing the bearing device by the apparatus according to claim
 18. 22.A bearing device, comprising: the bearing device having a radialrigidity value set by the method according to claim
 17. 23. An apparatusfor evaluating a rigidity of a bearing device including a bearing havingan inner ring, a shaft attached to the inner ring, an outer ring and anouter ring attaching member attached to the outer ring, comprising: aninput vibration unit for giving a radial input vibration to the innerring and the shaft attached to the inner ring; a vibration detectingunit for detecting a vibration of the outer ring attaching member; atransfer function calculating unit for calculating a transfer functionfrom an output of the vibration detecting unit and the radial inputvibration to determine a resonance frequency of the bearing device; anda rigidity calculating unit for determining a rigidity of the bearingdevice on the basis of the resonance frequency of the bearing devicedetermined by the transfer function calculating unit.
 24. An apparatusfor evaluating a rigidity of a bearing device including a pair ofbearing having an inner ring and an outer ring, a shaft attached to theinner ring and an outer ring attaching member attached to the outerring, comprising: an input vibration unit for giving a radial inputvibration to one of the each inner ring and both ends of the shaftattached to the inner ring; a pair of vibration detecting units fordetecting a vibration of one of the each inner ring and the both ends ofthe shaft attached to the inner ring; an adding unit for adding anoutput of the pair of vibration detecting units; a vibration detectingunit for detecting a vibration of the outer ring attaching member; atransfer function calculating unit for calculating a transfer functionfrom an output of the vibration detecting unit and the output of theadding unit to determine a resonance frequency of the bearing device;and a rigidity calculating unit for determining a rigidity of thebearing device on the basis of the resonance frequency of the bearingdevice determined by the transfer function calculating unit.
 25. Amethod for evaluating a rigidity of a bearing device including a pair ofbearing having an inner ring and an outer ring, a shaft attached to theinner ring and an outer ring attaching member attached to the outerring, comprising the steps of: giving a radial input vibration to one ofeach inner ring and both ends of the shaft attached to the inner ring;detecting a vibration of the one of each inner ring and both end of theshaft attached to the inner ring so that a first vibration detectingvalue and a second vibration detecting value are obtained; adding thefirst vibration and the second vibration so that an added value of thefirst vibration detecting value and the second vibration detecting valueis obtained; detecting a vibration of the outer ring attaching memberattached to the outer ring so that a third vibration detecting value isobtained; calculating a transfer function from the third vibrationdetecting value and the added value so that a resonance frequency of thebearing device is determined; and calculating a rigidity of the bearingdevice from the transfer function.
 26. An apparatus for producing abearing device including a bearing having an inner ring, a shaftattached to the inner ring, an outer ring and an outer ring attachingmember attached to the outer ring, comprising: an input vibration unitfor giving a radial input vibration to one of the each inner ring andthe shaft; a vibration detecting unit for detecting a vibration of theouter ring attaching member; a transfer function calculating unit forcalculating a transfer function from an output of the vibrationdetecting unit and the radial input vibration to determine a resonancefrequency of the bearing device; and a rigidity calculating unit fordetermining a rigidity of the bearing device on the basis of theresonance frequency of the bearing device determined by the transferfunction calculating unit.
 27. An apparatus for producing a bearingdevice including a pair of bearing having an inner ring and an outerring, a shaft attached to the inner ring, and an outer ring attachingmember attached to the outer ring, comprising: an input vibration unitfor giving a radial input vibration to one of each inner ring and bothends of the shaft attached to the inner ring; a pair of vibrationdetecting units for detecting a vibration of one of the each inner ringand the both ends of the shaft attached to the inner ring; an addingunit for adding an output of the pair of vibration detecting units; avibration detecting unit for detecting a vibration of the outer ringattaching member; a transfer function calculating unit for calculating atransfer function from an output of the vibration detecting unit and theoutput of the adding unit to determine a resonance frequency of thebearing device; and a rigidity calculating unit for determining arigidity of the bearing device on the basis of the resonance frequencyof the bearing device determined by the transfer function calculatingunit.
 28. A method for producing a bearing device including a pair ofbearing having an inner ring and an outer ring, a shaft attached to theinner ring and an outer ring attaching member attached to the outerring, comprising the steps of: giving a radial input vibration to one ofeach inner ring and both ends of the shaft attached to the inner ring;detecting a vibration of one of the each inner ring and the both ends ofthe shaft attached to the inner ring so that a first vibration detectingvalue and a second vibration detecting value are obtained; adding thefirst vibration and the second vibration so that an added value of thefirst vibration detecting value and the second vibration detecting valueis obtained; detecting a vibration of the outer ring attaching memberattached to the outer ring so that a third vibration detecting value isobtained; calculating a transfer function from the third vibrationdetecting value and the added value so that a resonance frequency of thebearing device is determined; and calculating a rigidity of the bearingdevice from the transfer function.